It's very common for spammers to try to use legitimate email addresses when sending their messages, so they can get through any spam filters that may exist. One of the most common tricks is to send the message from the same address you are sending it to. As such, we will not add your own Pobox addresses as trusted senders to your account.
This can cause some occasional problems for your account. For instance, if you send a test message to yourself from another ISP, it might get caught by your own aggressive filters. However, making your own address a trusted sender would let through any mail that has your email address forged as the From: header (which can be quite a lot of mail per day.) So, we will not add your own address as a trusted sender, or other addresses our analysis indicates would cause a large volume of spam to be sent to you.